Republican John McCain and Democrat Barack Obama slug it out again tonight at a showdown debate in the Arizona senator’s favored town-hall setting, which gives him his best chance to jump-start his sputtering campaign at a critical moment in the presidential election.

Fearing Mr. McCain is fast running out of time to structurally change the election’s strategic political focus, Republican strategists say that his only hope now is to make his rival’s judgment, inexperience, liberalism and tax increases the central issues in the campaign’s remaining weeks.

They say the antidote to Mr. Obama’s poll-driving lead on the economy is to attack him much more aggressively on his desire to take more tax money from people’s pockets.

“Obama’s tax-and-redistribute policies will not resurrect jobs, wages or the price of stocks in American retirement accounts,” said University of Maryland economist Peter Morici, who has been critical of the economic plans both candidates have proposed. “In fact, Obama’s policies may make economic conditions worse.”

The second of three presidential debates takes place at Belmont University in Nashville, Tenn., at a pivotal juncture for Mr. McCain, when his polls are sinking, the economy is teetering on the brink of recession, the stock market is in a nosedive and Mr. Obama is leading in at least half a dozen Republican red states from New Mexico to Florida.

The Gallup Poll’s national daily voter survey showed the Democratic candidate leading in the race by eight points, 50 percent to 42 percent, “the 10th straight day he has held a significant lead,” the polling organization said Monday.

Party strategists said it was also crucial for Mr. McCain to step up his attacks on Mr. Obama’s limited experience in government and his total absence from congressional negotiations to hammer out the kind of legislative compromises he says he would bring about as president.

“McCain has got to make the campaign about Barack Obama. There is this uneasiness among his supporters about whether he is tested enough, ready enough and whether people really know him,” said Republican campaign adviser John Brabender.

“McCain’s got to say that with everything going on in the world, my opponent hasn’t completed a full term in office other than in the Illinois state legislature, that he is not ready to lead, that he is a risk that Americans cannot afford to take,” Mr. Brabender said.

“People have to leave that debate saying, ‘Am I ready to pull the lever for Barack Obama,’ ” he said.

Mr. McCain has long been comfortable with the town-hall format that he has used throughout his two presidential campaigns, in which the audience submits questions to the candidate. He tried to get Mr. Obama to join him in 10 town-hall debates this summer at the end of the primary season, but the freshman senator turned him down.

“McCain’s better in this town-hall environment than Obama is because he’s been doing it forever and is comfortable answering people’s questions. It was a much higher risk for Obama back then because he needed the time to learn about the things he didn’t have to think about when he was running in the primaries against Hillary Clinton,” said Rich Galen, a veteran Republican campaign strategist.

Polls showed that Mr. Obama won last month’s first debate in Oxford, Miss, moderated by PBS anchor Jim Lehrer, but many analysts felt it was a split decision, with Mr. Obama clearly winning the first round on the economy, and Mr. McCain outscoring his rival when the subject turned to national security and foreign-policy issues. Mr. Lehrer asked all of the questions.

Tuesday night’s debate, which will focus entirely on economic and domestic-policy issues, will be moderated by NBC’s Tom Brokaw, with questions drawn from between 100 and 150 undecided likely voters in the audience.